This invention relates to apparatus for boring underground horizontal passageways.
Horizontally bored underground passageways for pipelines and utilities such as electrical distribution lines provide a safe, economical and environmentally responsible alternative to digging through or building over natural terrain and manmade obstacles.
A wide variety of underground passageway boring methods and apparatus for installation of utility cables, pipes and the like are known. Those known techniques include the use of a pneumatic impact piercing tool (sometimes termed a "mole") to punch a hole through soil without the need to excavate an open trench in which to lay the pipe or cable. Unguided moles are easily deflected off course by common anomalies, such as rocks, found in the soil. Improved moling apparatus for forming generally horizontal underground passages in the soil for a utility conduit or like are shown in U.S. Pat. Nos. 5,322,391 and 5,350,254. Such apparatus includes tool head structure with a base portion and a nose portion that is rotatably mounted on the base portion. Rotation of the base portion relative to the nose portion shifts the nose portion between a first position in which nose portion surfaces are symmetrical with respect to the tool axis so that the tool will move along a generally straight path and a second position in which nose portion surfaces are in asymmetric position with respect to the tool axis so that the tool will move along a generally curved path. That guided mole is preferably maintained in the straight line moling mode (symmetrical) tool configuration and shifted from the straight line configuration to a steered (asymmetrical) configuration by rotating the body portion relative to the nose portion (which tends not to rotate relative to the soil). The interface between the base portion and nose portion is exposed to soil materials, and it is desirable that that interface be maintained (for instance, clean and lubricated) such that the relative movement between the base portion and nose portion is without significant impairment.